This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. C. elegans has two sexes hermaphrodite(XX)and male(XO). Males only arise in the wild population at about 0.2% but hermaphrodites will use male sperm preferentially over their own sperm and some wild isolates use copulatory plugs to block sperm from other males.